【leetcode】Spiral Matrix II

 1 class Solution {
 2 public:
 3     vector<vector<int> >generateMatrix(int n) {
 4         int m=0;
 5         vector<vector<int> >a;
 6         a.resize(n,vector<int>(n));
 7         if(n==0)
 8             return a;
 9         int x=0;
10         int y=0;
11         m=a[0][0]=1;
12 
13         while(m<n*n)
14         {
15             while(y<n-1&&!a[x][y+1])
16             {
17                 m++;
18                 y++;
19                 a[x][y]=m;
20             }
21             while(x<n-1&&!a[x+1][y])
22             {
23                 m++;
24                 x++;
25                 a[x][y]=m;
26             }
27            
28             while(y-1>=0&&!a[x][y-1])
29             {
30                 m++;
31                 y--;
32                 a[x][y]=m;
33             }
34 
35             while(x-1>=0&&!a[x-1][y])
36             {
37                 m++;
38                 x--;
39                 a[x][y]=m;
40             }
41         }   
42 
43         return a;
44     }
45 };